The present invention relates generally to an apparatus and method for cutting spirally formed pipe, and more particularly, to an apparatus and method for cleanly cutting a relatively heavy-gauge pipe or a pipe having a relatively thick helical seam.
Several machines use inner and outer cutters to sever a pipe or tube. These cutters are typically rotatable and have a convex or circular cutting edge for engaging the pipe. During the cutting operation, the pipe is rotated relative to the cutters or the cutter(s) are revolved around the periphery of the pipe.
Some pipe cutting machines use these types of cutters to sever a continuously formed spiral pipe having a helical seam. Cutting machines of this type are disclosed in my U.S. Pat. Nos. 4,706,481, 4,823,579 and 4,924,684, issued Nov. 17, 1987, Apr. 25, 1989 and May. 15, 1990. In those machines, an inner knife is attached to a boom, and an outer knife is positioned outside the pipe. To cut the pipe, the outer knife is moved into an overlapping relationship with the inner knife. As the pipe rotates and moves axially, the overlapping knives move axially with the pipe and cooperate to cut the pipe.
U.S. Pat. No. 957,966 discloses an apparatus which cuts a continuously wound spiral paper tube. A plurality of rotatable outer knives are moved inward to engage the tube. The outer knives move axially and rotate with the tube during the cutting operation.
In E.P. Patent 353,622, a pair of outer knives are slidably mounted in a rotary unit which is positioned inside a cam ring. When a desired length of pipe has been reached, the feed of strip and formation of pipe is halted. The rotary unit is moved axially and the outer knives are forced radially inward to engage the pipe. The rotary unit is then rotated and the outer knives cooperate with a mandrel to cut the pipe.
Other pipe cutting machines use such inner and outer cutters for severing a pre-cut length of pipe. The device disclosed in U.S. Pat. No. 2,749,983 includes a plurality of outer cutters positioned outside a pipe stock. To perform a cutting operation, the pipe is rotated, the outer cutters are manually advanced into the pipe, and a plurality of inner cutters are moved radially outward to engage the inside surface of the pipe. In U.S. Pat. No. 3,268,137, an outer cutter wheel is moved inward until it engages a pipe and the cutter wheel is rotated around the stationary pipe to perform a cut. U.S. Pat. No. 3,913,430 discloses a device for cutting rings from a pipe. The pipe is manually placed inside a die, inner cutters are moved radially outward by levers to engage an interior surface of the pipe, and the cutters are revolved around the circumference of the pipe. In U.S. Pat. No. 3,839,933, an internal circular trimmer knife is moved radially outward to penetrate the wall of a stationary can body. The trimmer knife revolves around the axis of the can and interfaces with against an outer cutter ring during the cutting operation.
U.S. Pat. No. 1,635,807 discloses annular shearing dies with central openings of a size to receive a tubular member. To sever the tubular member, one of the dies rotates about the tubular member to impart a shearing action around the wall of the tubular member along a circumferential line.
None of these machines facilitates cutting a heavy gauge pipe or a pipe having a relatively thick helical seam. It is difficult to penetrate and cleanly cut such a pipe by rotating the pipe relative to the cutters or revolving cutters around the periphery of the pipe. A greater force is required to penetrate a thick helical seam, and firm guidance is required due to the irregular surface created by the thicker seam. Moreover, the increased stress required to penetrate such a thick seam tends to inhibit the continuous formation of the spiral pipe.